1. Field of the Invention
The present invention relates to a moving object detection method and apparatus for detecting moving objects, such as vehicles, using remote sensing techniques.
2. Description of the Prior Art
In a known system that debits tolls against vehicles traveling a toll road (refer to Japanese Patent Laid-Open Publication No. Hei 4-34684), the entering of a vehicle into a tollgate is optically detected, a toll bar is lowered at the exit of the gate at least until payment of the toll, and the toll bar is raised after confirmation of the toll payment. The greatest disadvantage of this system is that gates must be provided.
One motive of the present invention lies in solving the above-mentioned problem of the conventional system while another lies in improving some of the functions of an automatic debiting system (referred to as a xe2x80x9cpreviously proposed systemxe2x80x9d) proposed earlier by the assignee of the present application in Japanese Patent Application No. Hei 7-82523 and its corresponding U.S. patent application Ser. No. 08/661,703 now U.S. Pat. No. 5,602,395.
Solving the problem of the previously proposed system, which is the first motive, has already been achieved in the previously proposed system. In the previously proposed system, a gantry spanning a road is provided, and debiting against vehicles and debiting confirmation are executed through radio communications between antennas installed on the gantry and in-vehicle units (IU) in vehicles. Therefore, in the previously proposed system, it is not necessary to provide gates, thus resulting in such advantages as reductions in facility installations and maintenance costs, and prevention of traffic bottlenecks by allowing free lane travel. Furthermore, in operating an automatic debiting system, it is necessary to manage the system so that debiting is performed fairly against all vehicles traveling on the road. In the previously proposed system, steps can be taken to detect vehicles, such as those not carrying an IU, those carrying an IU for another vehicle type, or those for which payment was insufficient (collectively referred to hereinafter as illegal vehicles), and photograph their license plates. In this respect, the system management based on the above-mentioned object is satisfied. One method that is particularly effective in this respect among the various characteristic configurations in the previously proposed system is to detect vehicles using remote sensing techniques, and based on the result compared with that of debiting and debiting confirmation, to detect the various types of illegal vehicles. Specifically, the previously proposed system proposes a method for detecting positions where vehicles are located along a direction traversing the road, and to provide information, such as their detected positions (referred to hereinafter as xe2x80x9cdetected vehicle positionsxe2x80x9d) and their sizes (vehicle widths), for comparison with results such as debiting.
One point that must be taken into account when detecting, for example, the positions of vehicles along the direction traversing the road is false detection caused by any of a variety of factors. For example, if various types of noise (including factors caused by an operation or performance of vehicle detection devices, factors caused by interference among vehicle detection devices, and factors caused by environmental conditions of rain, snow, light, temperature, dirt, birds, and so forth) are generated during detection, false detection may result, such as objects other than vehicles being detected as vehicles or a single vehicle being detected as multiple vehicles. Furthermore, if an attempt is made to detect the positions of vehicles at a high resolution, for example, the likelihood of an above-mentioned noise-induced false detection generally increases and other errors become probable, for example, the detection of part of a vehicle, such as the angle or framework of a trailer""s rear, a mirror protruding from the side of a vehicle, or the outline of a vehicle having a complex profile in the horizontal plane, as second vehicle. Furthermore, when multiple vehicles travel side by side in close proximity to each other, it is also possible for these vehicles to be falsely detected as a single vehicle.
One object of the present invention lies in reducing or preventing false detection when detecting moving objects, such as vehicles, with sensors, such as distance sensors, by processing the positional information obtained from the concerned sensors using the profiles, movements, and so forth, of the moving objects.
A first aspect of the present invention is a moving object detection method and a second aspect is a moving object detection apparatus. In the first aspect, a process for detecting the existence of moving objects at multiple positions on a predetermined line by scanning on the concerned line, and a process for filtering moving object existence information obtained from this detection with filtering characteristics determined according to essential profiles of the moving objects and/or to moving object information obtained in a previous period are executed periodically. In the second aspect, the existence of moving objects at multiple positions on a predetermined line is periodically detected by scanning on the concerned line with sensors, and the moving object existence information obtained from the sensors at a certain period is filtered with filtering characteristics determined according to essential profiles of the moving objects and/or moving object information obtained in the previous period.
In the present invention, the original moving object existence information obtained from scanning and detecting on the line comprises information indicating whether or not a moving object exists at certain positions on the line. The original moving object existence information usually is susceptible to the effects of various types of noise, parts of vehicles (such as mirrors), moving conditions of the moving objects (such as traveling side by side), and so forth. Therefore, if the original moving object existence information is used as is, conditions, namely, false detection, may occur where the obtained information indicates with regard to a certain position, xe2x80x9ca moving object existsxe2x80x9d even though moving objects do not actually exist at that position (or should not be considered to exist), or xe2x80x9ca moving object does not existxe2x80x9d even though a moving object actually exists at that position (or should be considered to exist). The moving object existence information is filtered in the present invention to reduce the risk of false detection caused by the effects of various types of noise.
In the present invention, the filtering characteristics for use when filtering the moving object existence information are determined, for example, according to the essential profiles of moving objects. If the moving object existence information is filtered with filtering characteristics determined according to the relevant information, it becomes possible, from viewing the essential profile of a moving object, to correct the information when it was obtained indicating xe2x80x9ca moving object existsxe2x80x9d at a position where it should originally be xe2x80x9ca moving object does not existxe2x80x9d to information indicating xe2x80x9ca moving object does not exist,xe2x80x9d and conversely, to correct the information when it was obtained indicating xe2x80x9ca moving object does not existxe2x80x9d at a position where it should originally be xe2x80x9ca moving object existsxe2x80x9d to information indicating xe2x80x9ca moving object exists.xe2x80x9d Or, the filtering characteristics in the present invention may be determined according to the moving object existence information that was obtained in a previous period. If the moving object existence information is filtered with filtering characteristics determined according to the relevant information, it becomes possible, from viewing the continuity that should be maintained with the moving object existence information in a previous period, to correct the information when it was obtained indicating xe2x80x9ca moving object existsxe2x80x9d at a position where it should originally be xe2x80x9ca moving object does not existxe2x80x9d to information indicating xe2x80x9ca moving object does not exist,xe2x80x9d and conversely, to correct the information when it was obtained indicating xe2x80x9ca moving object does not existxe2x80x9d at a position where it should originally be xe2x80x9ca moving object existsxe2x80x9d to information indicating xe2x80x9ca moving object exists.xe2x80x9d In the present invention, these principles reduce the risk of false detection caused by various types of noise, for example, and achieve more precise moving object detection.
The present invention includes various preferred embodiments related particularly to bases for setting the filtering characteristics.
In a first preferred embodiment, when multiple positions (former) for which moving object existence information has been obtained indicating xe2x80x9ca moving object existsxe2x80x9d are less than or equal to a predetermined number of positions (latter) for which moving object existence information has been obtained indicating xe2x80x9ca moving object does not exist,xe2x80x9d the filtering characteristics were made to include a filling-up characteristic for correcting the contents of the moving object existence information in the latter to xe2x80x9ca moving object exists.xe2x80x9d In this embodiment, the filtering characteristics have been determined according to the essential profiles of moving objects, particularly a relative position where xe2x80x9ca moving object existsxe2x80x9d cannot be detected, namely, a profile having a gap. Therefore, if an attempt is made to detect a moving object having a gap when viewed from above, such as a motorcycle, a false detection of multiple moving objects due to the gap is less likely to occur.
In a second preferred embodiment, when multiple positions (former) for which moving object existence information has been obtained indicating xe2x80x9ca moving object does not existxe2x80x9d include a predetermined number or less of positions (latter) for which moving object existence information has been obtained indicating xe2x80x9ca moving object exists,xe2x80x9d the filtering characteristics were made to include a noise rejection characteristic for correcting the contents of the moving object existence information in the latter to xe2x80x9ca moving object does not exist.xe2x80x9d In this embodiment, a lower limit exists in the essential profiles of moving objects, particularly in a dimension along the direction of the line, thus, the filtering characteristics have been determined according to a property where moving object existence information indicating xe2x80x9ca moving object existsxe2x80x9d is hardly generated with regard to a small number of positions, or, isolated positions. Therefore, as an example, false detection of litter flying onto the road as a moving object becomes unlikely.
In a third preferred embodiment, when moving object existence information indicating xe2x80x9ca moving object existsxe2x80x9d has been obtained with regard to a larger predetermined number or greater of mutually adjacent positions, the filtering characteristics were made to include a maximum width checking characteristic for correcting the contents of the moving object existence information in positions selected at an interval of a smaller predetermined number from a predetermined number or greater of positions to indicate xe2x80x9ca moving object does not exist.xe2x80x9d In this embodiment, by utilizing the fact that in general an upper limit exists in the essential profiles of moving objects, particularly in a dimension along the direction of the line, the filtering characteristics have been determined according to a property where moving object existence information indicating xe2x80x9conly one moving object existsxe2x80x9d is not generated with regard to an extremely large number of mutually adjacent positions. Therefore, for example, false detection of multiple moving objects traveling side by side without sufficient space to be detected separately becomes unlikely.
In a fourth preferred embodiment, when mutually adjacent multiple positions (former) for which moving object existence information has been obtained indicating xe2x80x9ca moving object existsxe2x80x9d in a previous period and mutually adjacent positions (latter) for which moving object existence information has been obtained indicating xe2x80x9ca moving object existsxe2x80x9d in a recent period are at least partially overlapping, the filtering characteristics were made to include a width maintaining characteristic for correcting the contents of the moving object existence information in the recent period at positions included in the former and not included in the latter to indicate xe2x80x9ca moving object exists.xe2x80x9d In this embodiment, the filtering characteristics have been determined according to a continuity that should be secured with the moving object existence information obtained in a previous period, namely, a logical requirement where a dimension along the direction of the line should be maintained when the dimension has been obtained in the previous period. Therefore, for example, when an attempt is made to detect along the line a moving object having a gap as viewed from above, such as a motorcycle, false detection of one moving object as multiple moving objects due to the gap becomes unlikely, or when an attempt is made to detect along the line a moving object, such as a trailer having a framework at its rear portion, false detection of one moving object as multiple moving objects due to the framework becomes unlikely to occur.
In a fifth preferred embodiment, when moving object existence information has been obtained indicating xe2x80x9ca moving object does not existxe2x80x9d in a recent period with regard to positions for which moving object existence information has been obtained indicating xe2x80x9ca moving object existsxe2x80x9d in a previous period, the filtering characteristics were made to include a delaying characteristic for correcting the contents of the moving object existence information in the recent period at the positions to indicate xe2x80x9ca moving object exists.xe2x80x9d In this embodiment, the filtering characteristics have been determined according to the continuity and the complexity of moving object profiles which were taken into account in the fourth preferred embodiment. Therefore, even when sensing is unstable, for example, due to a moving object having a complex profile, false detection of a moving object""s dimension becomes unlikely.
In a sixth preferred embodiment, when moving object existence information indicating xe2x80x9ca moving object existsxe2x80x9d has not been obtained at a predetermined or greater frequency in multiple past periods with regard to a number of all mutually adjacent positions for which moving object existence information was obtained indicating xe2x80x9ca moving object existsxe2x80x9d in a recent period, the filtering characteristics were made to include a Y character profile prevention characteristic for correcting the contents of the moving object existence information at the multiple positions to indicate xe2x80x9ca moving object exists.xe2x80x9d In this embodiment, the filtering characteristics have been determined according to the essential profiles of the moving objects, particularly the complexity of their front ends, and the moving object existence information in multiple past periods. Therefore, for example, false detection, such as of a dimension, becomes unlikely, even for moving objects having complex front end profiles.
There are various preferred embodiments in the present invention in addition to the above, particularly with regard to filtering sequences.
In a seventh preferred embodiment, after the filling-up process in the first preferred embodiment and/or the noise rejection process in the second preferred embodiment, the width maintaining process in the fourth embodiment, the Y character profile prevention process in the sixth embodiment, the delaying process in the fifth embodiment and/or the maximum width checking process in the third embodiment are executed. According to this embodiment, causes of false detection (such as flying litter or other causes) related only to a comparatively small number of positions are first eliminated by the filling-up process and/or the noise rejection process, then causes of false detection (such as complexity of moving object profiles and moving object traveling states) related to a comparatively large number of positions are next eliminated by the width maintaining process, the Y character profile prevention process, the delaying process and/or the maximum width checking process. Therefore, compared to a case where these processes are executed in reverse sequence, the preventive effect of false detection is greater with the width maintaining process, the Y character profile prevention process, the delaying process and/or the maximum width checking process.
In an eighth preferred embodiment, after the width maintaining process in the fourth embodiment, the Y character profile prevention process in the sixth embodiment is executed. According to this embodiment, after a dimension along the line with regard to a comparatively detailed moving object profile was maintained in the width maintaining process, the Y character profile prevention process, which used the width information, is performed so that the effect of the Y character profile prevention process is further enhanced.
In a ninth preferred embodiment, after the filling-up process in the first embodiment, the noise rejection process in the second embodiment, the width maintaining process in the fourth embodiment, the Y character profile prevention process in the sixth embodiment and/or the delaying process in the fifth embodiment, the maximum width checking process in the third embodiment is executed. According to this embodiment, after the number of mutually adjacent positions providing moving object existence information indicating xe2x80x9ca moving object existsxe2x80x9d expands, the maximum width checking process is executed to enable multiple moving objects to be comparatively accurately separated and detected.